1. Technical Field
The invention relates to suspension methods and systems for vehicles such as trailers and trucks. More particularly, the invention relates to a suspension system using two or more rubber torsion axle assemblies that operate together. Specifically, the invention relates to a torsion axle assembly being linked to a second torsion axle assembly to improve axle-to-axle load equalization and provide for a softer ride.
2. Background Information
Torsion axles have been known for many years such as those shown in U.S. Pat. No. 2,998,981 for example. Torsion axles have proven to be extremely popular because if one wheel hits a bump or rut it can react independently of the other wheel which may not have hit a bump or rut at the same time. This torsion axle concept operates to keep a trailer moving as straight as possible while being towed behind a vehicle as well as absorbing some of the shock of the road over which it is passing with an independent suspension. This is contrasted with a straight axle where if one wheel drops into a rut or is slowed down for any reason while the other wheel of the trailer does not have the same experience at the same time, the trailer would tend to turn somewhat to allow the wheel that is on the flat part of the road to move forward while the wheel that is in the rut is restrained, therefore causing the axle not to be perpendicular with the direction of towing of the vehicle itself.
Torsion axles are constructed of a square axle in cross section with elongated rubber members disposed in-between the square axle and a larger outer tube. U.S. Pat. Nos. 5,161,814 and 5,820,156 disclose such a construction. One common torsion axle is a TorFlex® rubber torsion suspension system distributed by Dexter Axle. This type of torsion axle has independent and separate stub axles on each end which are part of spaced suspension assemblies mounting each of the wheels on the trailer frame to enhance the independent aspect of such an axle.
Torsion axles can also be constructed as in U.S. Pat. No. 5,163,701 which uses a plurality of elongated bars which can twist and bend but return to their original position after such twisting and bending. It is also known to use air bags for straight, non-torsion axles, such as shown in U.S. Pat. Nos. 3,784,221 and 5,427,404. While it is true that both the torsion axle technology and the air bag technology has been quite successful independently in making a smoother ride and enhanced the handling performances of vehicles having such suspension systems, these suspension systems still have their shortcomings and there is a need for improvement within the art.
Further, the vehicle suspension system of U.S. Pat. No. 6,340,165 combines the advantage of both the torsion axle and air spring into a single suspension assembly and has provided a more efficient and better performing suspension system than that believed provided by the systems using only a torsion axle or only an air spring. U.S. Pat. No. 7,758,056 improves on the system of U.S. Pat. No. 6,340,165 by providing a more rugged and compact structure by combining the pivot for both the torsion axle and connected spindle swing arm and the air spring mounting arm on a common axis. However, the spindle of the suspension of U.S. Pat. No. 7,758,056 rides at load position where the torsion axle is already partly compressed limiting the range of motion available of the spindle with respect to a no-load position. Also, when two or more torsion axle assemblies without any air suspension components are used in a suspension system there is no equalization of loads between the two or more torsion axle assemblies. Therefore, a better suspension system is needed.